This invention relates to ink jets, more particularly, to ink jets adapted to eject a droplet of ink from an orifice for purposes of marking on a copy medium.
It is generally desirable to employ an ink jet geometry which permits a plurality of ink jets to be utilized in a densely packed array so as to permit a reasonable area of a copy medium to be printed simultaneously as in the case of printing alphanumeric information. It is also desirable to utilize densely packed arrays of ink jets to achieve high quality in printing alphanumeric characters characterized by high speed or a high printing rate.
Difficulties can rise in achieving densely packed arrays because of the size or volume of the transducers which are utilized. For example, densely packed arrays can have a substantial mechanical cross-talk between channels. Moreover, large drive voltages may be necessary to appropriately energize transducers of the ink jets in the array and this can create undesirable electrical cross-talk particularly where the jets are densely packed.
Presently, considerable effort is being devoted to technology such as that disclosed in Stemme U.S. Pat. No. 3,747,120. While the Stemme patent does disclose a single jet as well as an array of jets, it is, in general, difficult to achieve densely packed arrays with this technology. Moreover, such arrays may employ a transducer configuration which results in a distributed pressure source applied to a volume of ink within an ink jet which may be undesirable, particularly in achieving stable satellite-free operation and high droplet velocity at low drive voltages.
Other difficulties which may be characteristic of this technology as well as other ink jet technology include: ink leaks which short out transducers, complex resonances in the transducer mounting structure which adversely affect jet operation, fabrication difficulties and unreliability in coupling energy from the transducer into the ink.
Another technology is disclosed in Elmquist U.S. Pat. No. 4,072,959 which does lend itself to a more densely packed array. As disclosed in this patent, a series of elongated transducers are energized by electrodes which apply a field transverse to the axis of elongation and the transducers are associated in a densely packed array of ink jet chambers. In this connection, it will be appreciated that the chambers are quite small so as to produce a high Helmholtz frequency as compared with the longitudinal resonant frequency of the individual transducers. Such a relationship can be undesirable since it is difficult to damp the longitudinal resonant frequency. Moreover, given the size of the Elmquist chambers, the proper control of the inlets to the chambers has no impact on improving the relationship between the Helmholtz frequency and the longitudinal resonant frequency of the transducer. As also disclosed in the Elmquist patent, each of the transducers is immersed in a common reservoir such that energization of one transducer associated with one chamber may produce cross-talk with respect to an adjacent chamber or chambers. In other words, there is no fluidic or mechanical isolation from chamber to chamber between the various transducers or more accurately, segments of a common transducer. In addition to the cross-talk problems, the construction as shown in the Elmquist patent poses a requirement for a non-conductive ink.